Batch freezer with cryogenic precooling apparatus and method

ABSTRACT

A freezer for a product includes a housing having a chamber therein with an atmosphere for reducing a temperature of the product; a cryogen refrigeration apparatus operationally associated with the chamber during a first cycle to pre-cool the atmosphere in the chamber; and a mechanical refrigeration apparatus operationally associated with the chamber during a second cycle to cool the atmosphere in the chamber when the first cycle is completed. A process is also provided.

CROSS-REFERENCE TO RELATED APPLICATIONS

This application claims the benefit of U.S. Provisional Application No. 61/859,335, filed Jul. 29, 2013.

BACKGROUND OF THE INVENTION

The present inventive embodiments relate to batch freezers, and chilling and freezing processes provided by same.

The initial cool down time of known batch freezer systems from room (or ambient) temperature to operating temperature restricts the usable operating time of the system during the day. Cool down times for a batch freezer can exceed one (1) hour. This limitation reduces the amount of product which can be frozen during a single shift or day and therefore, reduces overall efficiency of a plant freezing or chilling process.

During the initial cool down period of a mechanical batch freezer using conventional mechanical refrigeration (such as for example heat exchangers and condensers), the air inside the freezer (chilling or freezing atmosphere) is cooled by passing it across internal refrigeration coils. These coils are colder than the dew point temperature of the air inside the batch freezer. As a result, moisture from the air collects on these coils and freezes until the internal temperature of the system is cold enough so that all moisture in the air drops out. The accumulation of ice and snow on the refrigeration coils reduces the convective heat transfer between the internal air and the cods, which in turn results in significant inefficiencies in the mechanical refrigeration process.

In addition, moisture from the product is also released into the internal air during the initial cool down process of the mechanical batch freezer. Product dehydration is directly related to the duration of cool down from ambient to operating temperature of the batch freezer. If the freezer can be cooled down faster, the product experiences less dehydration which results in a more desirable final, saleable product for the customer and less moisture accumulation on the refrigeration coils.

BRIEF DESCRIPTION OF THE DRAWING

The FIGURE shows a sideview in cross-section of a batch freezer embodiment according to the present invention.

DETAILED DESCRIPTION OF THE INVENTION

To overcome the deficiencies of distinct mechnical and cryogenic freezers, there is provided a combined mechanical and cryogen freezer apparatus or assembly. The batch freezer embodiment of the present invention uses cryogen to provide 100% of the refrigeration for the initial cool down of the freezer and the product. Once the freezer reaches the desired operating temperature, the cryogenic apparatus portion shuts down and the mechanical refrigeration apparatus starts and operates for the duration of the production run. When a new batch of warm product is placed into the apparatus, the process outlined above repeats.

For purposes of the embodiments herein, mechanical refrigeration with a freezer assembly or apparatus is, for example, an apparatus or process by which heat is removed from a location using a heat exchanger over which a fluid flow is directed to provide a chilling and/or freezing flow from heat sink coils for a product such as for example a food product. That is, mechanical freezing provides refrigeration usually with a closed loop refrigeration cycle. The major components of a mechanical refrigeration apparatus or system include a compressor, condenser, expansion valve and evaporator. Electricity provides the power to the compressor which drives refrigerant through the closed loop cycle of the apparatus. Ammonia may be used as the refrigerant, but other substances can be used as well for the refrigerant. Mechanical temperature ranges usually can be brought down to −80° F.

For purposes of the embodiments herein, a cryogen freezer assembly or apparatus is for example one in which a cryogenic substance, such as liquid nitrogen or carbon dioxide, is provided such as by injection or spray, to a product to chill and/or freeze the product, such as a food product. Cryogenic freezing can provide refrigeration using a cryogenic fluid such as liquid nitrogen or carbon dioxide. Cryogenic freezing includes direct contact freezing of the product by having the refrigeration substance sprayed directly on to a surface of the product to be chilled or frozen, or in some applications submerged in the cryogen. Cryogen apparatus or systems are relatively simple to operate, easier to maintain and less costly than a comparable mechanical refrigeration apparatus or system. Cryogen refrigeration apparatus temperature ranges can be brought down to about −300° F. The cryogenic refrigerant may be dry ice, solid carbon dioxide (CO₂), liquid CO₂ or liquid nitrogen. The liquid cryogen can be sprayed directly onto the product, or the liquid cryogen can be sprayed or injected into a compartment where the products are contacted by the cryogen. The liquid may change phase to a gaseous mixture which can be circulated throughout the compartment.

The present freezer apparatus provides an initial cryogenic injection cycle during cool down or a pre-cool cycle which reduces such cool down time to be only 5-10 minutes, thereby providing the customer with greater opportunity for production during an operating day.

The independent cryogenic refrigeration injection assembly of the present embodiments is used to cool down the batch freezer apparatus. As the mechanical refrigeration system is not operating during the initial cryogen cool down period, no moisture will collect on the refrigeration coils. When the process reaches the desired operating temperature, the cryogenic system shuts off and the mechanical apparatus starts for a cool-down cycle. In effect, the cryogen assembly and the mechanical refrigeration assembly of the freezer apparatus are never in operation at the same time. All of the moisture in the air of the batch freezer has therefore dropped out and there is no possibility of accumulation on the mechanical refrigeration coils.

The rapid cryogenic pre-cool cycle or period provided by the present embodiments will bring the product surface temperature through the freeze point faster and minimize the overall dehydration loss of the food product within the process. Once the product's surface temperature is cooled past the freeze point, no more dehydration can occur and accordingly, the mechanical refrigeration assembly can be started.

Referring to the FIGURE, a batch freezer is shown generally at 10 and includes walls 11 (which can be insulated) to define a chamber 12 within the freezer for chilling or freezing of products 14, such as food products, therein. The chamber 12 includes a chilling and/or freezing atmosphere for the products 14. The food product 14 is chilled or frozen by being introduced into the chamber 12, usually by way of a moveable rack and tray assembly 16. Such rack assemblies 16 are known. The assembly 16 can support a plurality of the food products 14 for a freezing operation, after which the assembly is removed from the chamber 12, possibly to a remote location, for subsequent processing, such as packaging; while another assembly containing additional food products for freezing is rolled into the chamber for a subsequent freezing operation. An exhaust 18 is in communication with the chamber 12. The exhaust can be connected for operation with a blower (not shown) to remove cryogenic gas in the chamber 12 to an environment external to the freezer 10.

Disposed at one side of the chamber 12 is a heat exchanger 20 or mechanical condenser coils, and an air circulation device 22 such as at least one fan mounted, such as by way of example only, proximate and above the heat exchanger. Reference herein to an air circulation device 22 or fan includes the singular and plural of such elements. The fan 22 includes a housing 25 mounted within the chamber. The housing 25 supports the fan 22 to draw airflow to pass over the heat exchanger 20. The fan 22 can also be mounted below the heat exchanger 20 or in any other position for use in association with the heat exchanger and to sufficiently circulate atmosphere within the chamber 12. The heat exchanger 20 is charged with ammonia or a refrigerant such as R404A. The heat exchanger 20 and the fan 22 provide a mechanical refrigeration apparatus 15 or assembly.

A cryogen such as liquid nitrogen or carbon dioxide is introduced into the chamber 12 through cryogen piping 24 which extends to a cryogen injection manifold 26 disposed in the chamber. The cryogen piping 24 is provided with at least one valve 28 and if necessary a plurality of valves to each of which is mounted a transceiver 30 for a purpose to be described hereinafter. The cryogen injection manifold 26 includes at least one nozzle 32 and for many applications a plurality of nozzles mounted thereto for providing, by injection or otherwise, a cryogen spray 34 into the chamber 12 in a direction generally toward a position in the chamber where the rack and tray assembly 16 bearing the food products 14 is disposed. The cryogen piping 24, injection manifold 26 and spray nozzles 32 provide a cryogen refrigeration apparatus 17 or assembly. Such assembly can include for example the valves 28 and transceivers 30.

In effect, one embodiment of the present invention calls for the mechanical refrigeration apparatus 15 and the cryogen refrigeration apparatus 17 to be substantially disposed inside the freezer 12 for each such apparatus to be operationally associated with the chamber. Such construction provides for a unitary freezer apparatus 10 which can be moved or transported to alternate or remote locations for application and/or maintenance and repair as necessary. One such embodiment of the present invention has the cryogen injection manifold 26 disposed in the chamber 12 between the heat exchanger 20 and the rack and tray assembly 16 for efficient use of the volume of the chamber. It is understood that the position of the cryogen injection manifold 26 will be contingent upon the size of the heat exchanger 20 and the size of the rack and tray assembly 16, such that there is sufficient room for each and optimum coaction in order to realize the cool down and subsequent freezing of the food product 14.

A controller (PLC) 36 is provided to be in communication via a connection 37 with the transceivers 30 at the valves 28. The controller 36 is also in communication with a temperature sensor 38 which is in communication with an atmosphere in the chamber 12. The sensor 38 senses the temperature of the chamber 12 and communicates the temperature via a signal connection 39 to the controller 36.

In operation, the rack and tray assembly 16 containing the food product(s) 14 is positioned inside the chamber 12 of the apparatus 10. A door (not shown) to the chamber is shut. A temperature of the chamber 12 is sensed and communicated by the temperature sensor 38 via the connection 39 to the controller 36 which signals the transceivers 30 via the connection 37 to open the respective valves 28 to permit introduction of the cryogen through the piping 24 and into the cryogen injection manifold 26, wherein the cryogen is directed through the spray nozzles 32 as a spray 34 to impact the food product 14 and also charge the air flow 23 (a first cycle). A pressure or flow gauge 40 is in fluid communication with the cryogen in the piping 24 to indicate pressure of the cryogen or flow rate transiting the piping.

An air flow shroud 21 is disposed in the chamber 12 for coaction with the heat exchanger 20 and cryogen injection manifold 26. The shroud 21 is disposed in one embodiment proximate a lower portion of the heat exchanger 20 and, as shown in the FIGURE, extends from an inner surface of the wall 11 to the manifold 26. Such an arrangement of the air flow shroud 21 will direct air flow 23 drawn into the heat exchanger 20 to be deflected to pass in proximity to the cryogen injection manifold 26 to thereby be charged by the cryogen spray 34 to provide a cryogen chilled air flow 42 which is subsequently circulated by the fans 22 to be drawn again into the heat exchanger. The cryogen apparatus 17, shroud 21 and fan(s) 22 can be installed in different types of mechanical batch freezers and so the shroud and fan configurations can vary between manufacturers.

The controller 36 has been preset with the necessary temperature that the particular food product 14 will need for the duration of time that it will take in order to be sufficiently chilled or frozen to the specification required. For many applications, the controller 36 is set to achieve a temperature lower than the freezing point of the food product. The controller 36 will determine the length of time (e.g., 5-10 minutes) the cryogen is to be introduced into the manifold 26, either based upon a time sequence or when the temperature sensor 38 indicates that the temperature of the chamber 12 has reached a sufficiently low enough temperature to commence freezing operations. During the introduction of the cryogen into the chamber 12, neither the fan 22 nor the heat exchanger 20 is in operation, except however that the fan may be in operation during the initial cool down period or only a portion of the time during the initial cool down. During the initial cool down with the cryogen, the mechanical refrigeration apparatus 15 of the freezer apparatus 10 is not in operation.

As soon as the controller 36 senses that a desired or sufficient pre-cool down temperature has been reached by the introduction only of the cryogen, the controller 36 stops introduction of the cryogen, immediately after which the fan 22 and the heat exchanger 20—the mechanical refrigeration assembly 15—commences operation (the second cycle). During this time period of the second cycle there is no use of the cryogen. Also, for a process where cool down times for the product are known and repeatable, a timer (not shown) can be used to switch from cryogenic to mechanical operation, and back to cryogenic in a continuous, timed manner. For purposes of the embodiments herein, the pre-cool and cooling cycles may each begin when the previous cycle is completed or substantially completed. That is, the mechanical refrigeration cycle may commence when the cryogenic pre-cool cycle has completely ended, or upon cessation of the cryogenic pre-cool cycle such that same is coming to an end or winding down but has not completely finished or ended. Since the embodiments herein promote the efficient use of cryogen, the refrigeration permits the operator of the freezer to determine the most suitable time when to cease one cycle and commence with the other cycle.

The fans 22 draw the air flow 42 to pass over the heat exchanger as the air flow 23. The air flow 42 having been previously precooled by the earlier introduction of the cryogen, continues to be cooled as it passes across the coils of the heat exchanger 20 and is subsequently directed onto the food product 14 as the air flow 42, until such time as the designated amount of time has elapsed for sufficient chilling or freezing of the food product 14.

When the food product 14 has been sufficiently chilled or frozen, the cryogen exhaust 18 will vent the cryogen gas from the chamber 12. The cryogen is usually venting throughout the entire cool down process. When the atmosphere in the chamber 12 is vented and safe enough to enter, the fans 22 are stopped and the door is opened for removal of the rack and tray assembly 16 for subsequent processing. Another rack and tray assembly with other product for being chilled or frozen is moved into the chamber 12, the door is shut and the process begins again with the temperature controller 36 determining the amount of cryogen necessary for the precooling for the first cycle. After the cryogen precooling occurs, the introduction of cryogen is stopped and the fans 22 and mechanical heat exchanger 20 are activated to continue with the cool down or freezing of the food product 14 during the second cycle.

The present embodiments provide for the increased utilization of a mechanical batch freezer which results inasmuch as a 75% reduction in the amount of time necessary to cool down the food product for the required chilling or freezing. The cryogen delivery apparatus and method of the present embodiments increases the efficiency of the initial cool down of the food product because, in part, it is operating when the mechanical (heat exchanger and fans) portion of the freezer is not operating. There is therefore little if any snow or ice build up on coils of the heat exchanger 20. This results in increased efficiencies for the heat exchanger and the air flow 23 being moved over same.

In addition, the combined cryogen and mechanical freezing aspect of the present inventive embodiments provide for increased operating times of the mechanical refrigeration system because the snow and ice build up on the coils is substantially reduced if not eliminated. Therefore, the mechanical refrigeration components are able to maintain the set point temperature for a longer period of time so as to chill or freeze the food product to the temperature desired.

Moreover, food products frozen with the present apparatus 10 utilizing this process experience less dehydration. Since manufacturers sell food products by weight, less dehydration means a more saleable product for the end use customer.

It will be understood that the embodiments described herein are merely exemplary, and that one skilled in the art may make variations and modifications without departing from the spirit and scope of the invention. All such variations and modifications are intended to be included within the scope of the invention as described and claimed herein. Further, all embodiments disclosed are not necessarily in the alternative, as various embodiments of the invention may be combined to provide the desired result. 

What is claimed is:
 1. A freezer for a product, comprising: a housing having a chamber therein and an atmosphere in said chamber for reducing a temperature of the product; a cryogen refrigeration apparatus operationally associated with the chamber during a first cycle to pre-cool the atmosphere in the chamber; and a mechanical refrigeration apparatus operationally associated with the chamber during a second cycle to cool the atmosphere in the chamber when the first cycle is completed.
 2. The freezer of claim 1, wherein the cryogen refrigeration apparatus and the mechanical refrigeration apparatus are disposed in the chamber.
 3. The freezer of claim 1, wherein the cryogen refrigeration apparatus comprises a pipe extending into the chamber for introducing a cryogen into the atmosphere.
 4. The freezer of claim 3, further comprising a manifold connected to the pipe and having at least one outlet for the cryogen.
 5. The freezer of claim 1, wherein the mechanical refrigeration apparatus comprises a heat exchanger disposed in the chamber.
 6. The freezer of claim 1, further comprising an atmosphere circulation device disposed in the chamber for directing a flow of the atmosphere to contact the mechanical refrigeration apparatus.
 7. The freezer of claim 6, wherein the atmosphere circulation device is disposed proximate to the mechanical refrigeration apparatus.
 8. The freezer of claim 1, further comprising a shroud disposed in the chamber to direct airflow from the mechanical refrigeration apparatus to the cryogen refrigeration apparatus.
 9. The freezer of claim 8, wherein the shroud extends in the chamber from an inner sidewall of the housing to the cryogen refrigeration apparatus.
 10. The freezer of claim 1, further comprising: a cryogen inlet pipe in fluid communication with the cryogen refrigeration apparatus; at least one valve in the cryogen inlet pipe for controlling delivery of cryogen through said inlet pipe: and a controller in electronic communication with the at least one valve for controlling delivery of the cryogen through the cryogen inlet pipe.
 11. The freezer of claim 10, further comprising a temperature sensor in communication with the chamber and in electronic communication with the controller for providing a temperature signal to said controller.
 12. A process for reducing a temperature of a product in an atmosphere of a freezer, comprising: cryogenically reducing the temperature of the atmosphere with a cryogenic refrigeration apparatus operating during a first cycle for pre-cooling the atmosphere; and mechanically reducing the temperature of the atmosphere with a mechanical refrigeration apparatus operating during a second cycle for cooling the atmosphere when the first cycle is not operating.
 13. The process of claim 12, further comprising suspending the first cycle prior to commencing the second cycle.
 14. The process of claim 12, further comprising directing a flow of the atmosphere to contact the mechanical refrigeration apparatus.
 15. The process of claim 14, wherein the directing the flow is during the second cycle.
 16. The process of claim 12, further comprising sensing a temperature of the atmosphere for determining the operating of the first and second cycles.
 17. The process of claim 12, wherein the product comprises a food product.
 18. The process of claim 12, wherein the cryogenic refrigeration apparatus comprises a cryogen selected from the group consisting of liquid nitrogen and carbon dioxide. 